This invention relates in general to replacement body parts for humans and animals. In particular, the invention relates to a bioartificial intervertebral disc adapted for replacing a natural intervertebral disc in a spinal column of a human or animal.
Chronic low back pain is the primary cause of disability in active age groups of the society, playing a major role in the medical, social, and economic structure of industrial countries. The management of chronic low back pain is a prevalent problem to the clinician. It has been estimated that 70% of the population in the United States have experienced low back pain during their lives. While rest, medications, and therapy are the primary and preferred treatment methods, 4% of the population have still undergone surgical intervention. As the population ages, the problem will certainly grow.
Intervertebral disc degeneration and associated spinal disorders are a leading source of morbidity, resulting in substantial pain and increased health care costs. Disability of patients with low back pain creates extensive cost to the individual and society because of lost productivity and treatment costs, affecting millions of individuals. In the United States, the estimated health care cost for the treatment of chronic low back pain is 33 billion dollars per year with a total cost to society of greater than 100 billion dollars per year.
The intervertebral disc degenerates much earlier in life than other tissues. Disc degeneration begins in individuals in their twenties and increases throughout their adult life. While this does not always result in back pain, in many individuals there is significant back pain associated with disc degeneration. Disc degeneration can begin in the nucleus pulposus (NP) with a progressive decrease in proteoglycan content leading to dehydration of the NP. The swelling pressure resulting from high concentrations of proteoglycans in the NP helps to maintain disc height and contributes to the load-bearing ability of the disc. A loss of proteoglycans may directly affect the biomechanical function of intervertebral discs. It has been suggested that because the disc is the largest avascular tissue in the body, one reason for degeneration is a fall in transport of nutrients into the disc.
The current surgical treatment methods for intervertebral disc degeneration primarily involve the fusion of two vertebrae. Surgical stabilization and fusion of the spine have become increasingly common practice. Spinal fusion procedures are most commonly indicated when joint pain is a major symptom. Elimination of the relative motion between affected joints often reduces segmental pain. While there is a reduction or elimination of pain, surgical fusion leaves the patient with limited mobility.
One of the most recent developments for nonfusion surgical treatment is the total replacement of the intervertebral disc with a mechanical disc. Mechanical disc replacement designs have been classified into four categories: (1) low-friction sliding surface designs; (2) spring and hinge systems; (3) contained fluid-filled chambers; and (4) discs of rubber and other elastomers. The mechanical discs lack certain biological and mechanical properties of natural intervertebral discs.